1. Field of the Invention
The present invention relates to a method and apparatus for rendering a color image on a delta-structured display, and more particularly, to a method and apparatus for rendering an optimal color image on a delta-structured display apparatus, by using a sub-pixel rendering method with input images having different resolutions.
2. Description of the Related Art
In an image display apparatus, 3 sub-pixels, R, G, and B, are needed in order to express one pixel as the parts indicated by dotted lines in FIGS. 1 and 2. Accordingly, in a display apparatus, by manipulating the sub-pixels individually, a horizontal resolution can increase three times theoretically in the stripe topology of FIG. 2, and in the delta structure of FIG. 1, a horizontal resolution can increase 1.5 times and a vertical resolution can increase two times, theoretically. Meanwhile, when an image of a high resolution is desired to be displayed on a display apparatus having a low resolution, a jagged pattern occurs on the boundary of fine characters such as an Italic letter, in an ordinary individual pixel rendering method. This can be reduced by sub-pixel rendering, that is, individual manipulation of sub-pixels. However, the sub-pixel rendering has a drawback that it generates a color fringe on the boundary of an image. The color fringe is generated by a sudden change in the brightness value recognized between neighboring sub-pixels. This color fringe can be frequently found in the rendering of a diagonal line in the stripe structure and, this can be found in the rendering of a straight line in the vertical direction in the delta structure.
Among the existing patents written from the sub-pixel rendering perspective of an image display apparatus having this characteristic, there is a method of and apparatus for displaying a multicolor image by International Business Machines Corporation, U.S. Pat. No. 5,341,153, June 1988, in which a pixel of an input image is divided into R, G, B sub-pixels and rendered individually such that the effect of resolution improvement can be expected. In this technology, in order to render each sub-pixel, the average values of neighboring pixels about different central pixels of the input image corresponding to respective locations are used. However, though this technology improves the resolution, blurring is serious because a sub-pixel is rendered by the average value of the neighboring pixels, and a color fringe may occur in a sudden brightness change. Accordingly, rendering sub-pixels considering the characteristic of human eyesight is needed instead of the simple average of neighboring pixels.
When characters and graphics such as lines are desired to be rendered in a digital display apparatus such as an LCD, aliasing occurs in the sub-pixel rendering method. In a method and apparatus for rendering sub-pixel anti-aliased graphics, by Agfa Corporation, U.S. Pat. No. 6,384,839, September 1999, a method for reducing aliasing in a sub-pixel rendering method when such aliasing occurs is explained. In this technology, in order to determine the values of sub-pixels R, G, B, an LPF-filtered average value considering neighboring pixels of a corresponding location and the difference between the foreground and background are considered. This method is effective for a graphic image or characters in which the distinction between the foreground and the background is clear, but not appropriate to an image such as a natural image in which the distinction between the foreground and the background is not clear. Also, this method can be applied only to stripe topology color displays.
As described above, in the prior art technology of sub-pixel rendering for displaying a high resolution image on a low resolution display apparatus, blurring or color fringe occurs on the boundary, and the technology can be applied only to limited situations.